This invention relates to a twin-shaft pump having a working chamber which accommodates a pair of impellers and which is bounded by bearing plates for supporting the impeller shafts at the radial end faces of each impeller with the interposition of roller bearings or the like. The pump has a power drive which is connected to one of the shafts at the impeller end face from which the driven shaft extends.
A typical twin-shaft pump presently available on the market is disclosed in German Offenlegungsschrift (nonexamined published application) 1,939,717. The pump is a Roots vacuum pump (that is, it operates with interengaging lobed impellers) having the following principal structural components: a top closure, side plates or bearing plates on opposite sides of the working chamber, a housing and a motor flange (motor housing plate). These components have relatively large dimensions and are of relatively heavy weight. They are generally cast components involving labor-intensive finishing work. Installation and maintenance labor too, is intensive because the individual components have to be sealed and tightened to one another. Substantial structural space, large weight, problems in the sealing of the individual components as well as high expenses concerning finishing work, installation and maintenance are thus principal disadvantages of these pump arrangements. The lateral chambers in which the synchronizing drives and the connecting mechanism to the motor shaft are accommodated have relatively large dimensions and form detrimental dead spaces adjacent the working chamber. Furthermore, with increasing frequency, customers specify diverse sealing systems, drive systems or the like, dependent upon the intended particular use of the pump. The construction of known Roots pumps does not favor possibilities for a modular construction.
Further, in known Roots pumps, the shaft seals at the working chamber and the shaft bearings are arranged in an axial series behind one another. This necessitates a relatively large bearing distance, resulting in an increased structural length of the entire pump, an increased bending stress at the impeller shaft ends, an unfavorable dynamic behavior as well as a limited length-to-diameter ratio of the impellers. The structural space available for the working chamber shaft seal is between very narrow limits in the axial direction so that seal assemblies representing diverse sealing principles may be installed only at high expense.
To the twin-shaft pumps of the above-outlined type there further belong single-stage or multi-stage pumps whose impellers have other configurations, as disclosed, for example, in German Offenlegungsschriften 3,147,824 and 3,312,117. Screw-shaped impellers in twin-shaft vacuum pumps are also known. The invention furthermore relates to multistage twin-shaft vacuum pumps whose stages are equipped with differently configured impeller pairs.